st: bug in -xtmelogit-?

By accident I coded the following
xtmelogit depvar var1 || groupid: var2, cov(unstructured) var
Note that var2 is not in the equation, but I have specified it as
a random coefficient. After puzzling over my results for some time
I discovered my error, but I am surprised that -xtmelogit- did not
discover it for me. What exactly was it estimated for the variance
of the coefficient on -var2-? Is this a bug?
Jeph
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